Applicant hereby claims foreign priority under 35 U.S.C. xc2xa7 119 from German Application No. 101 38 674.5 filed Aug. 7, 2001.
The invention concerns a method for the control and regulation of the oil pressure-gas pressure relationship of diaphragm compressors.
Diaphragm compressors operate similarly to normal piston compressors, but with a separating diaphragm between the gas side and the oil side. The oil side is formed by the usual piston-cylinder unit, whose working and dead volumes are filled with oil. On the gas side are gas suction and pressure valves. The volume displaced by the oscillating movement of the piston is transmitted to the diaphragm, which then on its gas side takes on the suction, the compression and the exhaust of the gases. Since the oil pressure during the entire reciprocating movement corresponds to the course of the suction and compression pressure in the gas side, one can here also talk in terms of the operating mode of a piston compressor.
A small difference to piston compressors exists however in that in the case of diaphragm compressors a secondary oil circuit must be installed to allow compensation for the leakage of oil. For this purpose a compensation pump, driven by an eccentric on the crank shaft is used. This in synchronism with each piston stroke sprays a small amount of oil into the oil space of the compressor.
This amount must theoretically be exactly so large as the leakage at the compressor piston. Since this cannot be technically realized, always an injected amount of oil is used which is larger than the leakage. This in turn has the result that with each stroke of the compressor piston somewhat too much oil is contained in the oil space, which then at the forward dead point of the diaphragm (=engaging the cover), leads to an uncontrollable increase in oil pressure. To prevent this, it is further necessary that an oil overflow valve be used, which limits the oil pressure at the forward dead point of the piston to a value which is slightly above the maximum pressure of the gas.
The relationship between the gas pressure and the oil pressure at the forward dead point established by the oil overflow valve is the most important functional interrelationship in a diaphragm compressor. The reliable functioning of a diaphragm compressor is only achieved if the oil pressure at the forward dead point is always higher than the gas pressure. If this is not the case, the operating area of the diaphragm constantly wanders further toward the area of the aperture plate curve. If the diaphragm indeed touches the aperture plate, because of the given surface relationship, a fast rise in oil pressure occurs, which can lead to the lifting of the cover. Further, high loading peaks occur with very steep flanks which are transmitted to the crank shaft drive mechanism. The cavitation development produced thereby has a negative effect on the service life of the diaphragm.
Therefore, the control and regulation of the relationship between the gas pressure and the oil pressure, established by the oil overflow valve, comes to have a great significance.
Because of the rapid pressure change corresponding to the rotational speed of the compressor, the oil pressure spikes first of late have been able to be captured by some few SPS-controls. These values are then compared with fixed given boundary values, whereupon then in the case of a negative comparison result the compressor is turned off. In this case however only the absolute value of the oil pressure is compared with a shut-off value and not its relation to the momentary gas pressure. The sensing of the relationship is also important insofar as one cannot view the gas pressure as being of constant magnitude, and instead this pressure in the case of an engagement disorder can move into forbidden high areas, or, as can yet more often appear, with the failure of a compressor valve the gas pressure at an intermediate stage can become greatly increased and get into the range of the oil pressure spikes. This damage possibility cannot be controlled by the rigid supervision of the oil pressure absolute value.
Further, an old construction is known in which the gas pressure directly works as a spring supplemental tension force from above onto the spring plate of the oil overflow valve through a small piston. In this case, the spring in its fundamental position is only so pretensioned that it can be uncovered by about 30% of the maximum gas pressure. Further pretensioning results then by way of the gas pressure occurring in the system. The inadequacies of this system lie in the friction of the piston seal at high gas pressures and in the corrosion which can cause a total seizing of the small piston. Further the system is too slow to be able to follow rapid gas pressure increases during the starting phase of a compressor.
The effects on the compressor are fatal in the event they lead to one of the described disturbances in the control piston drive. Therefore, it comes to the situation that it cannot be allowed that the oil pressure suddenly comes to lie in the gas pressure area for even the shortest amounts of time, for within seconds from the engagement of the diaphragm work area with the aperture plate the feared damage occurs.
The object of the invention is to provide a method whereby the control of a given minimum relationship between gas pressure and oil pressure is assured and in a further construction stage a given relationship value is regulatable by a regulating circuit.
The object is solved by the sensing of the oil pressure-gas pressure relationship with one electronic pressure sensor on the oil side of the diaphragm head and another electronic pressure sensor in the pressurized gas conductor on the gas discharge side of the diaphragm head, with an associated electronic evaluation of both signals to thereby obtain the relationship of the two pressures, as well as by the production of a signal upon the falling of the relationship below a given minimum relationship value, and further by the possibility of maintaining a given relationship of oil pressure and a variable gas pressure controlled and regulated by the electronic evaluation and by a relief mechanism of the oil overflow valve controlled by this electronic evaluation.
The invention is illustrated in the drawings and is hereinafter described in greater detail.